The present invention relates in general to femoral shaft surgical rasps for use in forming an elongated canal in the femoral shaft of the thigh bone after amputation of a portion of the femur, into which a femoral head prosthesis member is inserted and fixed in the course of performing total and subtotal hip prosthesis surgery.
Heretofore, total hip prosthesis surgery has been performed wherein a prosthesis cup is fitted in the acetabulum, and a femoral prosthesis member or head prosthesis member, forming the femoral component of the total prosthesis, which comprises a stem or shank portion and an artificial head, is fixed in the femur shaft to provide a prosthetic hip joint. The fixation of the shank portion of the prosthesis (the head member) in the shaft of the femur has been attempted by forming an appropriately shaped canal or seating recess in the femur shaft and cementing the shank in the femur shaft, or by forming the canal, inserting the prosthesis shank, and drilling and installing bolts transversely through the femur shaft and the prosthesis shank. Considerable difficulties have been encountered in properly forming the canal in the femur for receiving the shank of the femoral portion or head porsthesis member in proper position in the femur shaft with rasps of conventional construction having the cutting prominences on all four surfaces of the rasp as in the case of the typical rasp used in the Harris total hip system (the components of which are advertised and sold by Howmedica, Inc. of Rutherford, N.J.), because of the proximity of soft tissue, such as the abductor muscles, to the path of reciprocative movement of the cutting portion of the rasp. Many surgeons detach the abductors from the greater trochanter to be able to move the abductors away from the path of the rasp so as to avoid damaging them, but the detachment of the abductors adds an aditional approximately six weeks to recuperation time.
Also, previous rasps have the cutting teeth on all four sides and therefore did not allow the surgeon to select the direction of maximum cutting. The direction of this cutting can be critical in proper seating of the prosthesis or trial hip, especially if there has been previous surgery. This is often the case, since many of these total hip prosthesis procedures are done as salvage procedures of old hip with many previous attempts at surgery.
My earlier U.S. Pat. No. 3,815,599 granted June 11, 1974 disclosed a femoral shaft surgical rasp designed to prepare the medullary canal of the femur to receive a shank of a femoral prosthesis member, wherein the rasp blade portion of the surgical rasp conformed generally to the shape of the shaft portion of the femoral prosthesis member, but had cutting prominences along one edge only of the rasping or working portion so as to present smooth surfaces in the other three directions to avoid traumatizing abductor muscles which are still attached to the femur and similar soft tissue. It has been found, however, that it is desirable in many instances to rasp in a manner that will cut only at the corners of the rasp device, preserving the soft cancellous bone to be compressed against the irregular rough surface of the stem of the prosthesis in order to leave bone intact that has a blood supply and provide an ingrowth of bone. The present state of the art practice is to ream the entire canal out and then force bits of cancellous bone down in beside the eventual stem of the femoral prosthesis member which would be essentially flat or slightly rounded.
I have discovered that it is desirable in many cases to limit the preparatory rasp cuts to the corner of the rasp device cutting portion, so as to leave the soft cancellous bone to be compressed against the stem of the femoral prosthesis device and obviate the necessity of packing bone around the stem, but rather leave bone intact which can compress against the stem of the prosthesis device with bone tissue that has a blood supply. In other words, it is desirable to not disturb the normal blood supply of the soft cancellous bone as it grows into the irregular rough surface of the final inserted stem of the femoral prosthesis device, and thus the four cutting edges of my rasp device are replica for the stem of the prosthesis eventually to be inserted.
An object of the present invention is the provision of a novel femoral shaft surgical rasp construction for use in performing total and subtotal hip prosthesis surgery, wherein the working or rasping portion of the rasp is in the shape of the shaft portion of the femoral prosthesis member to be inserted, and has cutting prominences only along the corners of the working or rasping portion of the rasp with smooth side and end surfaces between the toothed or cutting prominence portions so as to present smooth surfaces along the side faces and end faces of the working or rasping portion of the surgical rasp tool to avoid rasping or cutting the soft cancellous bone confronting those smooth side and end face portions. In this way the soft cancellous bone of the femur or other bone being rasped can be preserved so that it can press against the confronting surface of the shaft of the prosthesis device to be inserted and provide an ingrowth of bone at such confronting portions of the prosthesis shaft.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing illustrating preferred embodiments of the invention.